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  • New edelbrock carb causes backfires

    Installed a new 1406 on my 63 Avanti. Prior to that had the Carter which i simply couldn't get tuned properly. Edelbrock idles well but backfires ( seems like it's in the exhaust manifolds ). At normal cruising no backfiring. Have been thru the normal diagnostics - timing is 24 degrees BTDC. The backfiring increases at around 4000 RPM and the car jerks. Any ideas what else to check?

    Thanks

    Steve
    Avanti R-1 #2552
    Now set up as an R-3

  • #2
    I recently installed a new Edelbrock 1406 and i didnt have that problem. My backfiring was cause by the distributor I had was for a car with a computer.
    1957 Studebaker President Sedan 57H-W6 2606

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    • #3
      Wait a minute, this can't be an R2 Supercharged Avanti Engine since you are using a unsealed 1406 Carb. so what is the timing doing at 24 degrees? R1 timing is 4 degrees advance! [:0]

      StudeRich
      StudeRich
      Second Generation Stude Driver,
      Proud '54 Starliner Owner
      SDC Member Since 1967

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      • #4
        the 63 started life as an R-1 but is now running as an R-3 w/the air box.
        Avanti R-1 #2552
        Now set up as an R-3

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        • #5

          Sounds like you might be running tad lean. If you installed a Paxton, did you increase the jet size a couple notches?


          Bob Johnstone


          64 GT Hawk
          55 President State Sedan
          70 Avanti (R3)
          64 GT Hawk (K7)
          1970 Avanti (R3)

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          • #6
            So far running with the basic jets the 1406 came with...increasing the jets crossed my mind but thought the backfiring was due to some kind
            of over rich not overly lean set up.
            Avanti R-1 #2552
            Now set up as an R-3

            Comment


            • #7
              Best to get it richer before you burn the pistons down. Too much timing and too lean a jet size are recipe for disaster, don't ask me how I know!!!Might be helpful to call Edelbrock's tech line to have them give you a ballpark jet size for blown applications.

              Frank van Doorn
              Omaha, Ne.
              1962 GT Hawk 4 speed
              1963 Daytona Conv
              1941 Champion R-2 Powered Streetrod
              Frank van Doorn
              Omaha, Ne.
              1962 GT Hawk 289 4 speed
              1941 Champion streetrod, R-2 Powered, GM 200-4R trans.
              1952 V-8 232 Commander State "Starliner" hardtop OD

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              • #8
                Went to the Edelbrock site and checked out the 1406 specs - next sizes up are .101 & .104 and I've ordered both. Will set the timing back for the time being as well but think i swap the .101's in as soon as they arrive. Thanks for the advice guys.
                Avanti R-1 #2552
                Now set up as an R-3

                Comment


                • #9
                  A lean condition severe enough to cause a backfire usually shows up at cruising speeds as a surge and a flat spot under light acceleration.

                  I have an Edelbrock 1406 on my R2 with 98 jets in the front and 92's in the rear. Every engine is different but my car accelerated better with the 92 jet than both a 98 and a 95 that I had originally installed. Verfied the improvemant at the dragstrip so it wasn't just my 'asselerometer' thinking it performed better.

                  I'm assumming this is a full throttle issue since you said it's OK at cruise. Some things to consider...slipping blower belts, factory float levels not set properly causing a fuel starvation issue at high RPM, secondaries staying closed under boost ( happened with my carb causing severe surging at 4,000+ RPM )or the index hose from the blower to the fuel pump is off or leaking causing fuel starvation.

                  Timing is a possibility but at cruise you are running more total timing than at wide open, if you have vaccum advance connected, so again if you were too far advanced it would show up as a ping at part throttle acceleration and usually a surge or slight miss at cruise when the car is pulling the most vacuum. Of course, the 24 degrees was set at 1600 rpm and not idle, I assume.

                  The secondary issue I mentioned before does happen. The AFB and the E Carb's secondaries open via a spring. There's no hard linkage pulling them open it's only there to pull them shut. The spring actuation is there so the secondaries won't open when the choke is not completely open but still allowing you to put your foot to the floor and have a full range of motion on the primaries. Which leads to another thing to check which is the choke opening fully and not keeping the secondaries closed. The problem that I encountered was boost overpowering the spring on the secondaries. I finally tack welded the linkage so it's a full mechanical connection and all the weird surging I was experiencing disappeared.

                  BTW, Edelbrock tech will tell you their carbs are not recommended for blow through supercharging so don't expect any good advice.

                  ErnieR





                  1988 "Beater" Avanti---R2 R5388 @ Macungie 2006

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                  • #10
                    This forum may be of some help as well.


                    I have posted this question on another forum but no one had any suggestions - so I thought I would ask you guys. Can an Edelbrock carb be used for blow...


                    sals54
                    sals54

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                    • #11
                      Thanks Ernie - yes - problem is a flat/surge at cruise around 4000 RPM, especially up the long hill to the house. Went thru your list - supercharger to fuel pump line solid ( + i installed a light electric pump at the tank to ward off any vapor locks ), blower belts seem reasonably tight but could stand replacing, 24 BTDC was at 1600 RPM, looks like choke is adjusted and operating properly. I notice the Edelbrock site recommends .101 for the primary for blown use with 1406 so i've ordered those ( and the .104's for good measure ).
                      .101 is the next size up from stock so expect that should get me closer to proper a/f mix. Think I'll need different rods as well? See they recommend .070 X .042 rods....
                      Avanti R-1 #2552
                      Now set up as an R-3

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                      • #12
                        Check floats while you're in there. A fuel starvation problem will be worse uphill as fuel moves away from the primary jets. It's not unheard of to have anew carb that's not adjusted just right.



                        1988 "Beater" Avanti---R2 R5388 @ Macungie 2006

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                        • #13
                          My car didn't like the 101's. Black smoke after idling at a light and taking off. Again every set up is different. The lower a 70/42 rod will richen you even more than just the jet change. I think you have 75/47 in there now. As the numbers get smaller the carb gets richer. If you didn't buy the whole adjusting kit you may want to. I've been able to cure lean surge on my other edelbrock equipped cars with just a metering rod spring change. Heavier spring richer mixture. I don't envy you having to open up that air box for every adjustment



                          1988 "Beater" Avanti---R2 R5388 @ Macungie 2006

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                          • #14
                            Yeah - getting pretty good at popping the box on and off quickly....think I'll steal your idea and swap the rods first before messing with the jets - maybe I get lucky and solve it first try....well, I can dream.....
                            Avanti R-1 #2552
                            Now set up as an R-3

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                            • #15
                              Steve

                              Don't forget that the manual that came with the carb came with a chart that gives the jet/rod combo to move in steps toward lean or rich. The spring chart is also there.

                              I'm in the process of doing this with the 1806 in my Avanti.

                              If the manual was missing, it is available from the website.

                              Ernie is dead on about the metering rods and springs being the preferred way to start.

                              My apologies if you have all that in front of you.

                              Bob



                              ,

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